The present invention relates to a paper feeding mechanism for a continuous form printer that prints out information on continuous form paper.
Conventionally, continuous form printers which print out images in accordance with a so-called electrophotographic imaging method have been known.
According to the method, photoconductive material provided on a circumferential surface of a photoconductive drum of the printer is exposed to light which is modulated in accordance with image data, thereby a latent image being formed thereon. Then, toner is applied to the drum to form a toner image thereon (i.e., the latent image is developed). The toner image thus developed is transferred onto the paper, and the transferred toner image is fixed on the paper by a fixing device. Among such printers, one using continuous form recording paper has been known and widely used. An example of such a printer is disclosed in Japanese Patent Publication No. HEI 07-146625.
Typically, the continuous form paper is used in the form of fanfold paper, which is foldable continuous paper provided with sprocket holes on both end portions in its width direction of the paper.
As shown in the publication, in the printer using the fanfold paper, a tractor unit is provided to feed the paper. The tractor unit is provided with pins on a pair of belts located facing the end portions, in the width direction, of the paper. The belts are driven to move thereby the pins engaging with the sprocket holes of the paper pushing the paper to feed the same.
The tractor unit is provided on upstream side of a transfer unit where the toner image is transferred to the paper. In order to maintain tension of the paper during the imaging process within a certain range, a mechanism that applies the tension to the paper is generally provided on downstream side of a fixing unit, where the toner image is fixed. Typically, a pair of discharge rollers that function to discharge the paper out of the printer, and a tension plate that applies tension to the paper is provided between the tractor unit and the discharge rollers.
Some continuous form printers are configured such that an image is printed on a first page of the continuous form printer. That is, a toner image is transferred on the recording paper when a leading end of the continuous form paper is being fed from the tractor unit to the discharge rollers. In such a case, the continuous paper is firstly fed by the tractor unit. That is, each of the pins of the tractor unit pushes the upstream side edge of the corresponding sprocket hole. This state continues until the leading end of the paper is engaged with the rollers located on the upstream side and appropriate tension is applied to the paper.
When the leading end portion is engaged with the rollers on the upstream side, the tension plate is driven to push the paper to apply the tension thereto. At this stage, the paper is slightly pulled to move toward the portion where the tension plate contact the paper.
Since each pin of the tractor unit contacts the upstream side edge of the sprocket hole and the paper is pulled to move on the upstream side, the paper moves relative to the tractor unit toward the upstream side. Since the toner image is being transferred at this stage, the transferred image is deteriorated due to the shift of the paper.